The invention concerns a process for the conditioning of sensor signals utilized for the control and regulation of motion sequences, specifically for undercarriages of passenger cars and trucks.
Essential for the design of the undercarriage of an automobile is an efficient suspension and/or damping system. Such suspension and/or damping system normally consists either of a suspension arrangement with a fixed spring constant, paralleled by a damping device with adjustable damping, and/or of a suspension arrangement with adjustable spring constant. Furthermore, an essential element of such a suspension and/or damping system is an efficient process for control or regulation of the adjustable undercarriage. Based on information from sensor signals that monitor the suitability of the vehicle for road conditions i.e. road worthiness of the vehicle, such a process provides activation signals for the actuators of the adjustable undercarriage.
A suspension and/or damping system should ideally control or regulate the adjustable undercarriage in such a way that, for one, allowance is made for road safety and, for another, the passengers and/or shock-sensitive load of a vehicle are afforded maximum travel comfort. From the vantage point of the suspension and/or damping system, these are conflicting objectives. High travel comfort can be achieved through a maximally soft undercarriage adjustment, whereas with regard to high road safety a maximally hard undercarriage adjustment is desirable.
Known from the German patent application P 39 18 735.7 is a process for the damping of motion sequences on undercarriages of passenger cars and trucks. The activation signals for control or regulation of the adjustable undercarriage are essentially generated by the processing of sensor signals in filter arrangements. These filters are so conceived that the sensor signals that provide information on the roadworthiness of the vehicle will be influenced in their amplitude and/or phase pattern. Activation signals for the adjustable undercarriage are generated by this influencing, effecting thereby an adaptation to the current motional state of the vehicle, in such a way that at critical driving situations an undercarriage adjustment serving road safety and in uncritical driving situations a comfort adjustment is effected.
A comfort undercarriage adjustment can be achieved, for instance, in that the adjustable undercarriage features a maximally soft adjustment, i.e., for instance a slight damping in the case of an adjustable shock absorber. Control or regulation of the undercarriage that is more efficient by far, for instance in view of the bouncing, pitching and rolling oscillations of the vehicle body that determine the travel comfort, can be achieved through a so-called frequency contingent "skyhook" regulation such as described in the German patent application P 39 18 735.7 and in the German patent disclosure 37 38 284.
In the so-called skyhook control, the body acceleration is reduced thus bringing about an improvement of the travel comfort, whereas the road safety is not directly increased. Generally known in undercarriage control, this control concept is based on the model notion of a damping and/or suspension system which acts on vehicle body mass and is connected with an inertial fix point. Since such an inertial damping and/or suspension system cannot be directly realized in practice, the damping and/or suspension system arranged between the vehicle body mass and the wheel mass (refer to FIG. 1) is appropriately activated as a substitute.
Such a regulation or control is to be given preference whenever the momentary driving situation is not critical. In these driving situations, which in the normal vehicle operation usually occur much more frequently by far, not only relative path signals such as the spring deflection path are utilized for the control or regulation of the adjustable undercarriage, but also the absolute speed of the vehicle body is allowed for. The variables mentioned here will be explained in detail in FIG. 1.
An essential element for realizing the skyhook control is knowing the absolute vehicle velocity and/or of the buildup path. These variables are generally obtained from the signals of an acceleration sensor through appropriate signal conditioning.
Since each sensor has a limited working range outside of which the sensor does not deliver a useful signal, a signal conditioning is necessary, for instance in the form of band-pass filters. This band-pass filtering can be realized electronic-digitally, for instance by processing in computer units a differential equation that represents the transfer properties, or in an electronic-analog way by simulation of a differential equation representing the transfer properties, using electronic components. In order to obtain the useful signals of a sensor, the sensor signals are usually influenced in their frequency response by band-pass filters such as high-pass and low-pass filters. Moreover, depending on the requirements of the regulation or control with regard to the input data, integrating stages and/or differentiating stages are passed which, in turn, are of an electronic-digital or analog design.
When using the signals of a body acceleration sensor for the skyhook control, the integrity of the control or regulation is limited in the low-frequency range (about 0.1 to 1 Hz) of the vehicle body movements. This is attributable to the fact that the signals of the acceleration sensors used are filtered by filter units with high-pass type transfer behavior in order to avoid offset and drift effects.
For damping the inherent movement of the masses of a linear two-mass vibrator, the German patent disclosure 37 38 048 proposes to determine from the vehicle body acceleration path and spring deflection path or the spring deflection signals, respectively, the vertical absolute velocities of body and wheel. These absolute velocities are weighted and utilized for activation of the damping elements. In so doing, the German patent disclosure 37 38 048 is based on an ideal capturing and integration of the body acceleration.
The problem underlying the present invention is to provide an optimized processing of real vehicle body acceleration signals.